Images of the fourth Chengdu J-20 fighter prototype (2012) on the ground began appearing on Chinese internet sites in June 2014. It has since been revealed the aircraft made its first flight, which lasted around two hours, on July 26. The jet displays modifications introduced on the third aircraft (2011), which was first noted in January, including a faceted ‘bulge’ under the nose, possibly a housing for an electro-optical targeting system; refined air intakes; and a reprofiled upper tail from which a triangular section has been removed from the top of the trailing edge.